Regulating means for rotary piston compressor



1963 H. R. NILSSON' ETAL REGULATING MEANS FOR ROTARY PISTON COMPRESSOR 2Sheets-Sheet 1 Filed June 17, 1960 INVENTOR Oct. 29, 1963 H. R.'NILSSONETAL I r 3,108,739

REGULATING MEANS FOR ROTARY PISTQN COMPRESSOR Filed June 17, 1960 2Sheets- -Sh eet 2 United States Patent Ofi 3,108,739 REGULATING MEANSFOR ROTARY PISTON COMPRESSOR Hans Robert Nilsson, Ektorp, and LauritzBenedietus Schibbye, Saltsjo-Duvnas, Sweden, assignors to Svenska RotorMaskiner Aktiebolag, Nacka, Sweden, a corporation of Sweden Filed June17, 1960, Ser. No. 36,764 13 Claims. (Cl. 230138) The present inventionrelates to rotary piston, positive displacement compressors forcompressing elastic fluids, and has particular reference to that type ofsuch compressors disclosed in Nilsson, U.S. Patent No. 2,622,787,granted December 23, 1952.

Basically it is characteristic of such compressors that compressionchambers are formed by the intermeshing action of the helical lands andgrooves of male and female rotors mounted to rotate about coplanar axesin an appropriate housing structure, with the lands of the male rotorlying substantially outside of the pitch circle of the rotor and havinga wrap angle of less than one full turn or less than 360", while thelands of the female rotor likewise have a wrap angle of less than onefull turn, lie sub stantially within the pitch circle of the femalerotor.

It is further basically characteristic of such compressors that chevronshaped compression chambers are formed by communicating groove portionsof the cooperating rotors and the confronting wall portion of thehousing structure, the base ends of such chambers being defined by afixed transverse plane, usually coincident with the high pressure endwall of the housing structure, and the apex ends being defined by theplace of intermesh between the rotors, which moves axially away from theinlet ends of the rotors towards said fixed plane to cause the chambersto run out-to minimum volume at said plane as the rotors revolve. Thefixed plane is located at a place axially spaced from the inlet ends ofthe rotors where the high pressure or discharge port of the compressoris situated, the port being substantially confined to one side of theplane of the rotor axes, which may conveniently be designated the highpressure side of the compressor.

Similarly, it is basically characteristic of such compressors that onthe opposite or low pressure side of the compressor, where the lowpressure or inlet port of the compressor communicates with the inletends of the rotors, chevron shaped suction chambers are formed betweenrotor groove portions and confronting housing structure, which chambersexpand from minimum volume when the places of intermesh defining theapex ends of the chambers are at the inlet ends of the rotors to maximumvolume when the places of intermesh have moved axially away from theinlet ends of the rotors to the aforesaid fixed plane and the grooveportions forming the chambers have moved out of communication with eachother as the rotors revolve.

Compressors of the kind generally described above have been and arebeing utilized extensively in various fields of commercial application,including many fields in which part load or part capacity operation overextended periods of time is highly desirable. Operation at partialcapacity is of course readily accomplished through the simple expedientof throttling the intake of the compressor, but this kind of regulationentails throttling losses with consequent loss of efliciency which makessuch a kind of control undesirable for those applications where partload operation may constitute a substantial portion of the total time ofoperation.

In order to provide for more eflicient operation at partial capacity ofcompressors of the helical rotor type, than can be accomplished simplyby throttling the intake, various forms of valve devices have heretoforebeen pro- 3,168,739 Patented Oct. 29, 1963 posed, none of which,however, have proved to be wholly satisfactory from all standpoints eventhough effecting some improvement in efiiciency. Thus for example,capacity control valves of the kind disclosed in Lysholm, U.S. PatentNo. 2,459,709, granted January 18, 1949, which are interposed betweenstationary housing parts and the peripheries of the moving rotors,involve difiicul'ties of a mechanical nature such as the initialestablishment of and the maintaining of the very exact clearances whichare critical to the elficient operation of the machine and also requirethe presence of a lubricant between surfaces in direct communicationwith the compression chambers, a condition that could not be toleratedfor some uses (in the chemical industry, for example) of so-called drycompressors.

Other prior proposals have, for similar and other reasons, proved to beless than wholly satisfactory and it is therefore the principal andgeneral object of the present invention to provide new and improvedregulating means for controlling the operation of compressors of thekind under consideration in a way which will enable them to be operatedefficiently at variable part loads down to a relative small fraction offull load or full capacity. It is a further object to accomplish suchregulation by valve means which introduce no throttling effects andlosses, and which moreover are not only simple in mechanicalconstruction but also of with nature that critical clearances betweenstationary and rotating parts are easily established initially andreadily maintained over long periods of use.

Other and more detailed objects of the invention will become apparent asthe ensuing description of suitable embodiments of apparatus forcarrying the invention into effect proceeds, with reference to theaccompanying drawings, in which;

FIG. 1 is a longitudinal section, partly in elevation, of a suitableembodiment of apparatus for carrying the invention into effect;

FIG. 2 is a section taken on the line 22 of FIG. 1;

FIG. 3 is a view similar to FIG. 1 of another embodiment of apparatusembodying the invention;

FIG. 4 is a section taken on the line 4-4 of FIG. 3;

FIG. 5 is a side elevation partly in section of still another embodimentof the invention; and

FIG. 6 is a section taken on the line 6-6 of FIG. 5.

Referring now to the drawings, and more particularly to FIGS. 1 and 2thereof, the compressor comprises a stationary housing structure 18having a barrel portion providing a working space composed of twointersecting cylindrical bores 20 and 22 with coplanar axes which in theembodiment illustrated are parallel. The housing structure is funtherprovided with portions forming end walls 24 and 26 defining the axiallength of the working space. A male rotor 10 provided with helical lands12 is rotatably mounted in bone 20, and a female rotor 14 likewiseprovided with helical lands 16 is rotatably mounted in bore 22 with thelands of the two rotors in intermeshing engagement. As shown, the landsand grooves of the rotors have a wrap angle of less than one full turn(less than 360), the lands of the female rotor lying substantiallyentirely within the pitch circle of the rotor while the pitch circle ofthe male rotor lies substantially at the root circle of the lands of therotor. Also the lands of the male rotor are convexly curved and ofsubstantially circular profile, while the lands of the female rotor arecorrespondingly concave, as shown, the construction being advantageouslyas disclosed in Nilsson, U.S. Patent No. 2,622,787, granted December 23,1952.

The housing structure provides a low pressure inlet channel 32terminating in an axial inlet port 28 and further provides an outlet ordischarge port 30 delivering to the discharge channel 34. Port 30 islocated at the plane of the high pressure end wall 26 and is confined toone side of the plane through the axes of the rotors, which side mayconveniently be referred to as the high pressure side of the compressor.

The compressor is driven by means of a power input shaft 36,conveniently driving the male rotor, and the rotors may be connected bytiming gears so that the female rotor is driven in synchronized relationto the male rotor, such gears not being shown but being convenientlylocated in a gear housing appearing at the right of FIG. 1.

A part of the inlet channel 32 extends along the bottom of thecompressor past the barrel portion of the housing to communicate with avalve chamber 38 located beyond hte high pressure end wall 26. Twoseries of separate valve means 40 and 42 are provided in the highpressure end wall to-provide selective communication between the workingspace formed by the bores in the barrel portion of the housing and thevalve chamber 38. As will be seen from the figures these valve means areof the poppet valve type opening outwardly from the working space intothe valve chamber and as will be observed particularly from FIG. 2 thevalve ports for the several valve means are located in spaced relationperipherally around the axes of the two rotors at radial distancestherefrom corresponding to the radial distances of the grooves of therespective rotors from their axes. For reasons which will later becomemore clear, these valve means are hereinafter referred to as bleed valvemeans.

The operation of the apparatus, in accordance with the principles of theinvention is as follows, it being assumed that the rotors are rotated inthe directions indicated by the arrows 44 and 46 in FIG. 2. As therotors revolve in the directions indicated, the suction chambers areformed at the bottom or low pressure side of the compressor, beinginitiated at zero volume at the plane of the low pressure end wall 24and expanding in chevron shaped formation as the places of intermeshbetween the rotors move from the low pressure wall 24 to the highpressure wall 26. At the latter wall the communicating groove portionsforming each such chamber pass out of communication with each other andthe peripheral extent of the inlet port 28 is such that during theentire inlet phase of the cycle the chambers are in communication withthe inlet port, so that when the grooves pass out of communication witheach other they are completely filled to full capacity with workingfluid. The grooves, thus filled to capacity with working fluid at inletpressure, continue to turn until places of intermesh between grooves areestablished on the high pressure side of the compressor at the inlet endthereof to form the high pressure compression chambers which diminish involume progressively as the places of intermesh move axially from theinlet to the outlet end of the compressor.

If, at the time of intermesh to form the compression chambers and duringthe compression portion of the cycle following that time, the valvesconstituting the bleed valve means are all closed, then the fullquantity of fluid inducted into the compressor will be compressed andejected through the discharge port. Under such conditions the compressorwill operate at full capacity.

If, on the other hand, one or more of the bleed valves is open at thetime when any given compression chamber is formed, further rotation ofthe rotors following that time, instead of resulting in compression inthat chamber, will result in rejection of a portion of the previouslyinducted fluid through the open valve ports in the high pressure endwall and the return of that rejected fluid to a low pressure zone whichin the examples shown constitutes the inlet passage of the compressor.Such rejection of previously inducted fluid will continue until the endsof the grooves forming the chamber pass out of registry with which everones of the bleed ports that are open. When that occurs, actualcompression in the chamber is initiated and continues until thecompression chamber comes into communication with and discharges throughthe high pressure discharge port.

Thus it will be seen that in accordance with the principles of thepresent invention, control of the capacity of the compressor is effectedby means which involves no throttling or other restriction of the flowof the working fluid, with consequent elimination of losses occasionedby that kind of operation, but effects the desired control by freelyadmitting working fluid up to the full capacity of the compressor andthereafter freely rejecting a portion of that fluid from the compressorbefore work is expended thereon in compressing it. It will thus beevident that the control is effected efficiently even down to smallfractional capacities.

As will be more or less evident from FIG. 2, the type of regulationwhich will be effected by this embodiment of the apparatus is of thestep-bystep type rather than by continuously variable control. Thereason for this is of course that the ends of the grooves forming thecompression chambers pass out of registry in step-by-step fashion withthe several ports which control the degree of reduction in the capacityof the compressor that is being effected. It is further to be noted inconnection with FIG. 2 that the ports of the valve 40 cooperating withthe male rotor are spaced apart peripherally further than are the ports42 cooperating with the female rotor. The reason for this is that in theembodiment illustrated the male rotor is provided with four lands whilethe female rotor is provided with six. Consequently, the female rotorturns at only two-thirds the speed of the male rotor and the spacing ofthe valve ports as shown is required if the same timing relation is tobe maintained between the ports and the grooves for each rotor. Also,since each compression chamber is formed of two communicating grooveportions, one in each rotor, it will be evident that the bleeding ofeach compression chamber can be adequately effected by one set of bleedvalve ports cooperating with one of the rotors. However, in order toprovide the most unrestricted flow it is advantageous to use two seriesof such valve means in the form as illustrated.

Since in the embodiment illustrated the area of the ex haust port isconstant, it follows that the volumes of the compression chambers willbe constant at the time when they come into registry with the exhaust ordischarge port. Since the capacity regulation eifected in accordancewith the present invention results in differing compression chambervolumes at the times when actual compression commences, it will beevident that in the structure illustrated, regulation of the capacity ofthe compressor will also result in a variation in the compression ratioeffected. If it is desired to maintain a constant compression ratio atall capacities, or to effect other desired variations in the compressionratio, these results may readily be obtained by other means well knownin the art which form no part of the present invention.

FIGS. 3 and 4 illustrate another embodiment of apparatus which ingeneral is similar to and functions to give the same kind of regulationas the embodiment illustrated in FIGS. 1 and 2. The only essentialdifference in the present embodiment is the use of radially movableslide valves 48 and 50, instead of the poppet type valves shown inFIG. 1. In both of these embodiments, the faces of the valves are insealing proximity to the end faces of the rotors, with appropriaterunning clearances between the parts.

FIGS. 5 and 6 illustrate a further embodiment of apparatus employingslide valves 52 and 54 similar to the slide valves 48 and 50 of themodification shown in FIG. 4 but with these valves arranged differentlyso as to provide for progressive regulation rather than step-by-stepregulation of the kind effected by the arrangement shown in FIG. 4.

In the present arrangement only one bleed valve is provided forcooperation with each rotor, these valves being arranged to movegenerally tangentially with respect to the axes of the respectiverotors, and controlling valve ports each of which communicates with theinlet passage 32 of the compressor. It is believed mere inspection ofFIG. 6 of the drawings will be sufiicient to make it apparent how theprogressive regulation is effected by these valves rather than thestep-by-step regulation which is effected by separate valves operatingto control separate spaced apart valve ports that are passedsuccessively by the grooves forming the compression chambers.

From the foregoing it will be evident that the principles of theinvention may be carried into efiect with numerous different specificforms of apparatus operating in diiferent fashions to provide eitherstep-by-step or con tinuous progressive regulation. It is accordingly tobe understood that the invention is not to be considered as beinglimited to the forms of apparatus herein before described by way ofillustration, but is to be considered as embracing all forms ofapparatus falling within the scope of the appended claims.

We claim:

1. A rotary piston, positive displacement, elastic fluid compressorcomprising a housing structure providing a barrel portion havingintersecting bores with coplanar axes and a high pressure end wall andfurther providing a high pressure discharge port at said end wall, atleast the major part of said port being located on one side of the planeof said axes constituting the high pressure side of the compressor andan inlet communicating with the ends of said bores remote from said highpressure end wall, male and female rotors provided with intermeshinghelical lands and grooves having an effective Wrap angle of less than360 rotatably mounted in said bores and operative to sequentially formwith the confronting portion of the housing structure on the lowpressure side of said plane a series of chevron shaped suction chambersexpanding from minimum volume at the inlet ends of the rotors to maximumvolume as the places of intermesh forming the apexes of said chambersmove axially away from said inlet ends as the rotors revolve until thelands and grooves move out of mesh at said high pressure end wall, saidlands and grooves subsequently intermeshing at-the inlet ends of therotors on said high pressure side as the rotors revolve to sequentiallyform with the confronting portion of the housing structure a series ofchevron shaped compression chambers running out to minimum volume atsaid high pressure end wall as the places of intermesh forming theapexes of said compression chambers move axially away from the inletends of the rotors to said high pressure end wall, and regulating meansfor bleeding said grooves to a low pressure zone to control the capacityof the compressor comprising bleed port means in said high pressure endwall, said port means being located to register with each of the groovesof at least one of said rotors in positions of the groove out ofcommunication with said discharge port from the position at which thecompression chamber of which the groove forms a part is at maximumvolume to a position at which the volume of the last mentioned chamberhas port means comprises a been reduced to the extent required to effectthe desired regulation and bleed valve means capable of selectiveadjustment during operation of the compressor to close said port meansto determine the volumes of said compression chambers when compressionis initiated therein to thereby regulate the capacity of the compressor.

2. A compressor as defined in claim 1 including conduit means forconducting fluid bled through said ports to said zone of low pressure.

3. A compressor as defined in claim 2 in which said conduit meansdelivers the bled fluid to the inlet of the compressor.

4. A compressor as defined in claim 1 in which said regulating meanscomprises a rectilinearly movable bleed valve member for controllingeach bleed port. 7

5. A compressor as defined in claim 4 in which each said valve member isof the poppet type.

6. A compressor as defined in claim 5 in which said port means comprisesa plurality of ports spaced peripherally about the axis of at least oneof said rotors.

7. A compressor as defined in claim 6 in which said port means comprisesa plurality of ports spaced peripherally about the axes of both saidrotors.

8. A compressor as defined in claim 4 in which each said valve member isof the slide valve type.

9. A compressor as defined in claim 8 in which each said valve member ismovable generally radially with respect to the axis of the associatedrotor.

10. A compressor as defined in claim 9 in which said port meanscomprises a plurality of ports spaced peripherally about the axis of atleast one of said rotors.

11. A compressor as defined in claim 9 in which said plurality of portsspaced peripherally about the axes of both of said rotors.

12. A compressor as defined in claim 1 in which said regulating meanscomprises a bleed port extending generally tangentially with respect toat least one of said rotors and a sliding type bleed valve membermovable generally tangentially to provide progressive regulation of thevolumes of said compression chambers when compression therein isinitiated.

13. A compressor as defined in claim 12 in which said regulating meanscomprises a bleed port and cooperating valve member for each rotor.

References Cited in the file of this patent UNITED STATES PATENTS2,266,820 Smith Dec. 23, 1941 2,358,815 Lysholm Sept. 26, 1944 2,459,709Lysholm Jan. 18, 1949 2,504,230 Smith Apr. 18, 1950 2,519,913 LysholmAug. 22, 1950 2,580,006 Densham Dec. 25, 1951 2,622,787 Nilsson Dec. 23,1952 2,656,972 Rathman Oct. 27, 1953 FOREIGN PATENTS 272,910 SwitzerlandApr. 16, 1951 1,158,976 France Feb. 3, 1958

1. A ROTARY PISTON, POSITIVE DISPLACEMENT, ELASTIC FLUID COMPRESSORCOMPRISING A HOUSING STRUCTURE PROVIDING A BARREL PORTION HAVINGINTERSECTING BORES WITH COPLANAR AXES AND A HIGH PRESSURE END WALL ANDFURTHER PROVIDING A HIGH PRESSURE DISCHARGE PORT AT SAID END WALL, ATLEAST THE MAJOR PART OF SAID PORT BEING LOCATED ON ONE SIDE OF THE PLANEOF SAID AXES CONSTITUTING THE HIGH PRESSURE SIDE OF THE COMPRESSOR ANDAN INLET COMMUNICATING WITH THE ENDS OF SAID BORES REMOTE FROM SAID HIGHPRESSURE END WALL, MALE AND FEMALE ROTORS PROVIDED WITH INTERMESHINGHELICAL LANDS AND GROOVES HAVING AN EFFECTIVE WRAP ANGLE OF LESS THAN360* ROTATABLY MOUNTED IN SAID BORES AND OPERATIVE TO SEQUENTIALLY FORMWITH THE CONFRONTING PORTION OF THE HOUSING STRUCTURE ON THE LOWPRESSURE SIDE OF SAID PLANE A SERIES OF CHEVRON SHAPED SUCTION CHAMBERSEXPANDING FROM MINIMUM VOLUME AT THE INLET ENDS OF THE ROTORS TO MAXIMUMVOLUME AS THE PLACES OF INTERMESH FORMING THE APEXES OF SAID CHAMBERSMOVE AXIALLY AWAY FROM SAID INLET ENDS AS THE ROTORS REVOLVE UNTIL THELANDS AND GROOVES MOVE OUT OF MESH AT SAID HIGH PRESSURE END WALL, SAIDLANDS AND GROOVES SUBSEQUENTLY INTERMESHING AT THE INLET ENDS OF THEROTORS ON SAID HIGH PRESSURE SIDE AS THE ROTORS REVOLVE TO SEQUENTIALLYFORM WITH THE CONFRONTING PORTION OF THE HOUSING STRUCTURE A SERIES OFCHEVRON SHAPED COMPRESSION CHAMBERS RUNNING OUT TO MINIMUM VOLUME ATSAID HIGH PRESSURE END WALL AS THE PLACES OF INTERMESH FORMING THEAPEXES OF SAID COMPRESSION CHAMBERS MOVE AXIALLY AWAY FROM THE INLETENDS OF THE ROTORS TO SAID HIGH PRESSURE END WALL, AND REGULATING MEANSFOR BLEEDING SAID GROOVES TO A LOW PRESSURE ZONE TO CONTROL THE CAPICITYOF THE COMPRESSOR COMPRISING BLEED PORT MEANS IN SAID HIGH PRESSURE ENDWALL, SAID PORT MEANS BEING LOCATED TO REGISTER WITH EACH OF THE GROOVESOF AT LEAST ONE OF SAID ROTORS IN POSITIONS OF THE GROOVE OUT OFCOMMUNICATION WITH SAID DISCHARGE PORT FROM THE POSITION AT WHICH THECOMPRESSION CHAMBER OF WHICH THE GROOVE FORMS A PART IS AT MIXIMUMVOLUME TO A POSITION AT WHICH THE VOLUME OF THE LAST MENTIONED CHAMBERHAS BEEN REDUCED TO THE EXTENT REQUIRED TO EFFECT THE DESIRED REGULATIONAND BLEED VALVE MEANS CAPABLE OF SELECTIVE ADJUSTMENT DURING OPERATIONOF THE COMPRESSOR TO CLOSE SAID PORT MEANS TO DETERMINE THE VOLUMES OFSAID COMPRESSION CHAMBERS WHEN COMPRESSION IS INITIATED THEREIN TOTHEREBY REGULATE THE CAPACITY OF THE COMPRESSOR.